1. Field of the Invention
This invention relates to an etching method of organic insulating films, and particularly to an etching method suitable for etching organic insulating films used in the production of semiconductor devices.
2. Description of the Related Art
[Prior Art 1]
As a method for etching an organic insulating film while preventing the microtrenching without using etch stop layer, for example, the method of WO 01/15213 A1 (JP-A-2001-60582) is known. The gazette of the above-mentioned patent gives the following description.
Thus, the wafer temperature is maintained at 20-60xc2x0 C., in accordance with the processing. Then, a gaseous mixture of N2, H2 and Ar is introduced into the processing chamber. The inner pressure of the processing chamber is adjusted to 500 mTorr or more substantially, and preferably 500-800 mTorr substantially. Then, a radio-frequency voltage having a frequency of 13.56 MHz and a power of 600-1,400 W is applied to the lower electrode, and a radio-frequency power having a frequency of 60 MHz and a power of 600-1,400 W is applied to the upper electrode. By taking such a measure, a high-density plasma is generated in the processing chamber and, due to the plasma, contact holes of a desired shape are formed in the insulating layer between layers of wafer made of an organic low-dielectric constant material.
Further, the same gazette as above makes the following mention, too.
A treating gas containing at least a nitrogen atom-containing gas and a hydrogen atom-containing gas is introduced into the processing chamber, and the inner pressure of the vacuum processing chamber is adjusted substantially to 500 mTorr or more to carry out etching of the organic layer film formed on the wafer to be etched placed in the processing chamber. As the material constituting the organic film, a low-dielectric constant material having a relative permittivity of 3.5 or less is preferable. The inner pressure of the vacuum processing chamber is preferably kept at 500-800 mTorr substantially.
By using a gas containing at least a nitrogen atom-containing gas and a hydrogen atom-containing gas as the processing gas and adjusting the inner pressure of the vacuum processing chamber substantially to 500 mTorr or higher, microtrenching can be prevented without using etch stop layer and the mask-selection ratio can be enhanced. Such a technique is especially effective for processes which require to stop the etching in the midst of an organic layer film, such as the dual damascene process, or the like.
It is possible to use N2 as the nitrogen atom-containing gas or to use H2 as the hydrogen atom-containing gas, if desired. In the gazette referred to above, there are mentioned some examples in which the N2/H2 flow rate ratio (N2/H2) is 400 sccm/400 sccm, 200 sccm/200 sccm, and 100 sccm/300 sccm.
[Prior Art 2]
As another method for etching an organic insulating film, the method of JP-A-2000-252359 is known. The following description is given in the gazette thereof.
An insulating film (insulating film) between layers made of an organic dielectric film such as polyallyl ether is subjected to etching, while forming a CN group-containing reaction product, etc. by the use of an NH group-containing ion or radical generated from a gas plasma made from a mixture of hydrogen and nitrogen or an ammonia-containing gas.
The etching process of the insulating film between layers is carried out by means of ECR type (Electron Cyclotron Resonance type) plasma etching apparatus under conditions of, for example, a substrate-provided electrode temperature of 20xc2x0 C., a xcexc-wave power (2.45 GHz) of 2,000W, a pressure of 0.8 Pa, an RF power of 300 W, by using NH3 as an etching gas at a flow rate of 100 sccm.
In the etching process mentioned above, it is also possible, if desired, to carry out the etching process by the use of a gas plasma comprising a gaseous mixture of hydrogen and nitrogen at a flow rate (N2+H2) of, for example, 100 sccm at a H2/N2 flow rate ratio of, for example, 75/25 sccm.
By carrying out the etching using NH group-containing ion or radical, an insulating film containing an organic dielectric film can be subjected to an anisotropic etching without forming a damage layer causing defective conduction, while suppressing side etching, while maintaining a high etch rate of about 450 nm/minute, without bringing about a reduction of throughput, and rapidly.
By such a technique, it is also possible to etch an insulating film containing an organic insulating film to open contact holes. This technique is applicable also to an etching process for forming trench for interconnect wiring such as damascene process, or to an etching process for simultaneously opening trench for interconnect wiring and contact hole such as dual damascene process, etc.
Further, if etching process of insulating film between layers is carried out under various conditions [(a) N2=100 sccm, (b) N2/H2=50/50 sccm and (c) H2=100 sccm] and emission spectra are measured, an NH peak observable neither in the case (a) using N2 gas nor in the case (c) using H2 gas is observed in the case (b) using N2/H2 mixture. Further, as for CN peak, the peak intensity observed in the case (b) using N2/H2 mixture is higher than the peak intensity in the case (a) using N2 gas and in the case (c) using H2 gas.
Further, if the flow rate ratio of etching gas is so varied that N2/H2=100/0 to 50/50 to 0/100 sccm and the relative etch rate (the etch rate at N2/H2=100/0 sccm is taken as 1) and the emission spectral intensity ratios between the light-emitting components (CN, NH, N2, CH, H) at varied flow rate ratios are measured, it is found that the etch rate and the emission spectral intensity ratio between CN and NH are roughly the same in the behavior.
In the recent years, a damascene process using copper has been used as a method for forming a wiring on semiconductor elements. As an application of the damascene process, a dual damascene process can be referred to. In the prior dual damascene, an etch stop layer has been used for preventing the sub-trenching which is sometimes called xe2x80x9cmicrotrenchingxe2x80x9d, at the time of forming a trench for interconnect wiring leading to the organic insulating film functioning as an insulating film between layers. Since an etch stop layer has a high dielectric constant, however, it is attempted today to lower the dielectric constant without using any etch stop layer.
According to the former prior art mentioned above (JP-A-2001-60582), etching of organic layer film is performed while keeping the inner pressure of vacuum processing chamber at 500 mTorr (ca. 66.5 Pa) or above, and preferably at 500-800 mTorr. According to this etching method, however, inner pressure of the processing chamber is very high, and hence this method is expected to have the following problems: (1) in the case of samples having a large diameter such as 300 millimeter wafer, the waste gas generated as a reaction product from the wafer surface cannot sufficiently be removed at the central part of wafer, so that the etch rate within the wafer surface is not uniform, (2) the quantity of reaction product is so large that controlling the shape of trench and hole is difficult, and (3) the quantity of reaction product is so large that inside of processing chamber is apt to be soiled, which reduces reproducibility of the etching treatment. Accordingly, a measure for solving these problems have to be taken when the processing is to be carried out at a high processing pressure.
On the other hand, the latter prior method (JP-A-2000-252359) is known as a method for etching an organic insulating film at a low processing pressure (0.8 Pa) which makes it unnecessary to consider the above-mentioned problems in the etching process at a high processing pressure. The latter prior method, however, pays no consideration for the problem occurring when an organic insulating film of dual damascene process is etched while preventing microtrenching without using etch stop layer.
According to the latter prior art, an organic insulating film is etched with an NH group-containing ion or radical generated by gas discharge or the like in a hydrogen-nitrogen gas mixture or ammonia gas mixture as a processing gas, while forming a CN group-containing reaction product, etc. However, this technique is unable to prevent the microtrenching without using etch stop layer at any flow rate ratio of hydrogen-nitrogen mixed gas or ammonia-containing gas.
The etching method of the latter prior art is a method in which attention is paid to the fact that etch rate and CN/NH emission spectral ratio are roughly the same in behavior. Accordingly, this method has a problem that the optimum condition of etching cannot be selected on the basis of CN/NH emission spectral intensity ratio, and the optimum condition for etching an organic insulating film while preventing micro-trenching without using etch stop layer cannot be selected.
The phenomenon that a microtrenching (sometimes called xe2x80x9csub-trenchingxe2x80x9d, too) is formed and thereby the bottom surface of the trenches or holes of the etched part become impossible to flatten is attributable to the following fact. The etch rate is higher in the neighborhood of sidewall of trenches and holes than in the central parts of the trenches and holes due to collision of the incident ion originated from the plasma against the sidewall, caused by the slight taper of the sidewall of trenches and holes which are the part to be etched, followed by concentration of the incident ion into the neighborhood of sidewall of trenches and holes, or due to a re-deposition of various reaction products formed by the etching to the central parts of trenches and holes.
It is an object of this invention to solve the problems mentioned above by providing an etching method of organic insulating film which makes it possible to perform etching of an organic insulating film while suppressing the re-deposition of reaction products onto inner walls of processing chamber and preventing the microtrenching.
The above-mentioned object can be achieved by an etching method of organic insulating film which comprises generating a plasma from a molecular gas containing hydrogen atom and nitrogen atom, measuring the emission spectral intensity ratio between hydrogen atom and cyan molecule in the plasma, and carrying out the processing while keeping the measured value of the ratio at a prescribed value or under.
In this invention, there is used a plasma in which the emission spectral intensity ratio CN/H between the emission spectrum of hydrogen (H) at a wavelength of about 486 nm and that of cyan molecule (CN) at a wavelength of about 388 nm is 1 or less.
Further, the above-mentioned object can be achieved by generating a plasma from hydrogen gas and nitrogen gas or ammonia gas, and performing an etching method of organic insulating film while controlling the flow rate of hydrogen gas so that the emission spectral intensity ratio between hydrogen atom and cyan molecule in the plasma comes to a prescribed value or under.
The processing is carried out while controlling the processing pressure at a constant value.
Further, the above-mentioned object can be achieved by supplying a nitrogen gas and a hydrogen gas or a molecular gas containing hydrogen atom and nitrogen atom into an etching process chamber in which is placed a sample to be etched forming an organic insulating film, adjusting the inner pressure of the etching process chamber to a pressure lower than 10 Pa, thereby generating a plasma in which the intensity ratio CN/H between an emission spectrum of hydrogen atom (H) at a wavelength of about 486 nm and an emission spectrum of cyan molecule (CN) at a wavelength of 388 nm is 1 or less, and processing the sample to be etched with said plasma.
For generating of the plasma, a hydrogen gas and a nitrogen gas are used, and the mixing ratio of the hydrogen gas to the nitrogen gas is adjusted to 10 or more. Further, total flow rate of the hydrogen gas and nitrogen gas is adjusted to 200 cc/minute or more.
Alternatively, a hydrogen gas is used as the molecular gas containing hydrogen atom, an ammonia gas is used a the molecular gas containing nitrogen atom, and the mixing ratio of the hydrogen gas to the ammonia gas is adjusted to 10 or more. Further, the total flow rate of the hydrogen gas and the ammonia gas is adjusted to 200 cc/minute or more.
According to another embodiment of this invention, the above-mentioned object can be achieved by generating a plasma in the process chamber, measuring the emission spectral intensity ratio between cyan molecule and hydrogen atom in the plasma, controlling the flow rate-controlling valves so as to keep the measured value at a prescribed value or under, and etching the sample to be etched, by the use of an apparatus equipped with a sample stand on which a sample to be etched can be placed, an air-leakless process chamber into which an etching gas is fed, a vacuum pump evacuating the inner space of process chamber to a reduced pressure, flow rate-controlling valves which can control the flow rates of hydrogen gas and nitrogen gas or a molecular gas containing hydrogen atom and nitrogen atom, a gas exhaust rate-controlling valve which is placed between the vacuum pump and the process chamber to control the exhaust rate of the etching gas fed into the process chamber, a circuit and an electric source to which the electric power for generating a plasma from the etching gas in the process chamber can be applied, and a vacuum gauge for measuring the pressure in the process chamber. The flow rate-controlling valves are controlled so as to increase the flow rate of hydrogen gas. Further, the gas exhaust rate-controlling valve is controlled so as to keep constant the inner pressure of the process chamber.
The sample to be etched is etched while controlling the output of electric source for generating a plasma from the etching gas so as to keep the measured value at a prescribed value or under. The electric source is controlled so as to increase the output and thereby to increase generation of hydrogen atom in the plasma.
Further, an electric source capable of inputting a bias voltage to the sample to be etched is connected to the sample stand, and the electric source is controlled so as to lower the bias voltage and thereby keep the measured value at a prescribed value or under.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.